Autoimmune diseases occur when an organism's immune system fails to recognize some of the organism's own tissues as “self” and attacks them as “foreign.” Normally, self-tolerance is developed early by developmental events within the immune system that prevent the organism's own T cells and B cells from reacting with the organism's own tissues. Major histocompatibility complex (MHC) cell surface proteins help regulate these early immune responses by binding to and presenting processed peptides to T cells.
This self-tolerance process breaks-down when autoimmune diseases develop. In such diseases, the organism's own tissues and proteins are recognized as “autoantigens” and are attacked by the organism's immune system. For example, multiple sclerosis is believed to be an autoimmune disease, which occurs when the immune system attacks the myelin sheath, whose function is to insulate and protect nerves. It is a progressive disease characterized by demyelination, followed by neuronal and motor function loss. Rheumatoid arthritis (“RA”) is also believed to be an autoimmune disease, which involves chronic inflammation of the synovium in joints with infiltration by activated T cells, macrophages and plasma cells, leading to a progressive destruction of the articular cartilage. It is the most severe form of joint disease. The nature of the autoantigen(s) attacked in rheumatoid arthritis is poorly understood, although collagen type II is a candidate.
Some believe that multiple sclerosis and rheumatoid arthritis are inherited disorders because these diseases occur more frequently in individuals carrying one or more characteristic MHC class II alleles. For example, inherited susceptibility for rheumatoid arthritis is strongly associated with the MHC class II DRB1 *0401, DRB 1 *0404, or DRB 1*0405 or the DRB1*0101 alleles. The human leukocyte antigens (HLA) are found on the surface of cells and help determine the individuality of tissues from different persons. HLA genes are located within the MHC on chromosome 6. The MHC region expresses a number of distinctive classes of molecules in various cells of the body, the genes being, in order of sequence along the chromosome, the Class I, II and III MHC genes. The Class I genes consist of HLA genes, which are further subdivided into A, B and C subregions. The Class II genes are subdivided into the DR, DQ and DP subregions. The MHC-DR molecules are the best known; these occur on the surfaces of antigen presenting cells such as macrophages, dendritic cells of lymphoid tissue and epidermal cells. The Class III MHC products are expressed in various components of the complement system, as well as in some non-immune related cells.
Another example of an autoimmune disease is Systemic lupus erythematosus (SLE), or lupus, which is a debilitating autoimmune disease characterized by the presence of an array of autoantibodies, including antibodies to double stranded DNA, to nuclear protein antigens and to ribonucleoproteins. SLE affects approximately 1 in 2000 individuals (U.S. 1 in 700 women). The disease primarily affects young women, with a female-to male ratio of approximately 9:1.
Systemic lupus can affect almost any organ or system of the body. Systemic lupus may include periods in which few, if any, symptoms are evident (“remission”) and other times when the disease becomes more active (“flare”). Most often when people mention “lupus,” they are referring to the systemic form of the disease.
Corticosteroids are the mainstay in treating systemic autoimmune disorders. Life threatening, severely disabling manifestations of SLE are treated with high doses of glucocorticoids. Undesirable effects of chronic glucocorticoids include an array of prominent adverse effects such as cushingoid habitus, central obesity, hypertension, infection, capillary fragility, hirsutism, accelerated osteoporosis, cataracts, diabetes mellitus, myopathy and psychosis. In addition to corticosteroid toxicity, patient compliance to a dosage regimen also poses a serious problem.
Cytotoxic agents are also used for controlling active disease, reducing the rate of disease flares, and reducing steroid requirements. Undesirable side effects of the latter include bone marrow suppression, increased infections with opportunistic organisms, irreversible ovarian failure, alopecia and increased risk of malignancy.
Programmed death 1 (PD-1), an inhibitory receptor expressed on activated lymphocytes, is thought to be involved in autoimmune diseases, such as SLE. PD-1 has two ligands: PD-1 ligand 1 (PD-L1), which is expressed broadly on hematopoietic and parenchymal cells, including pancreatic islet cells; and PD-L2, which is restricted to macrophages and dendritic cells.
SLE is an inflammatory disease for which to date there is no definitive diagnostic tool, treatment or cure. The disease results in acute and chronic complications. The only current treatments available are palliative, aimed at relieving acute symptoms and preventing chronic complications, often with profound side effects. The need for new detection methods and treatments for autoimmune diseases, such as SLE are manifest.